Le Chatelier’s Principle

• What does Le Chatelier's principle describe?

  Position of equilibrium in reversible reactions
• What factors affect the position of equilibrium?

  Temperature, pressure, and concentration
• What does the position of equilibrium refer to?

  Ratio of reactant to product particles
• When is the equilibrium said to lie to the left?

  If there are more reactants than products
• When is the equilibrium said to lie to the right?

  If there are more products than reactants
• What happens to the position of equilibrium if conditions change?

  It shifts to counteract the change
• What is the reaction for the production of ammonia?

  Nitrogen and hydrogen produce ammonia
• What is the overall energy change of the forward reaction for ammonia production?

  -92 kilojoules per mole
• What does a negative energy change indicate about the forward reaction?

  It is exothermic and releases energy
• What must the backward reaction be if the forward reaction is exothermic?

  It must be endothermic
• What happens to equilibrium if the temperature is decreased?

  It moves in the exothermic direction
• What does it mean if the equilibrium moves to the right?

  There are more ammonia particles
• What happens to equilibrium if the temperature is increased?

  It moves in the endothermic direction
• How does pressure affect the position of equilibrium?

  It shifts to reduce pressure
• What side does equilibrium shift to if pressure is increased?

  To the side with fewer molecules
• How many molecules are on the left side of the ammonia reaction?

  Four molecules
• How many molecules are on the right side of the ammonia reaction?

  Two molecules
• What happens to equilibrium if pressure is decreased?

  It shifts to the side with more molecules
• What happens if more nitrogen is added to the system?

  Equilibrium shifts to the right
• What are the effects of changing temperature, pressure, and concentration on equilibrium?

  • Decreasing temperature shifts equilibrium to exothermic direction
  • Increasing temperature shifts equilibrium to endothermic direction
  • Increasing pressure shifts equilibrium to side with fewer molecules
  • Decreasing pressure shifts equilibrium to side with more molecules
  • Adding reactants shifts equilibrium to product side
• How does Le Chatelier's principle apply to reversible reactions?

  • Predicts shifts in equilibrium position
  • Counteracts changes in temperature, pressure, and concentration
  • Helps understand dynamic equilibrium in reactions
• What does Le Chatelier’s Principle state?

  That if a closed system at equilibrium is subject to change, the system will move to minimise the effect of that change.
• What are the 3 changes the system will move to minimize?

  Concentration

  Temperature

  Pressure (for gases)